Electrically powered exit signs, traffic signals, task lights and other devices are widely used. Fluorescent lamps are used to provide illumination in typical electrical devices for general lighting purposes because they are more efficient than incandescent bulbs in producing light. A fluorescent lamp is a low pressure gas discharge source, in which light is produced predominantly by fluorescent powders activated by ultraviolet energy generated by a mercury plasma forming an arc. The lamp, usually in the form of a tubular bulb with an electrode sealed into each end, contains mercury vapor at low pressure with a small amount of inert gas for starting. The inner walls of the bulb are coated with fluorescent powders commonly called phosphors. When the proper voltage is applied, the plasma forming an arc is produced by current flowing between the electrodes through the mercury vapor. This discharge generates some visible radiation. The ultraviolet in turn excites the phosphors to emit light.
Two electrodes are hermetically sealed into the bulb, one at each end. These electrodes are designed for operating as either “cold” or “hot” cathodes or electrodes, more correctly called glow or arc modes of discharge operation. Electrodes for glow or cold cathode operation may consist of closed-end metal cylinders, generally coated on the inside with an emissive material. Conventional cold cathode lamps operate at a current on the order of a few hundred milliamperes, with a high cathode fall or voltage drop, something in excess of 50 volts. CCFLs are not appreciably affected by starting frequency because of the type of electrode used CCFLs emit light in the same way as to standard hot electrode lamps. The latter type operate as normal glow discharges and their electrodes are uncoated hollow cylinders of nickel or iron. The cathode fall is high and to obtain high efficacy or power for general lighting purposes, conventional lamps are made fairly long, about 2-8 feet, with a diameter of about 25-40 millimeters. About 2000 volts is required for starting these conventional lamps and about 900 to 1000 volts for running.
The advantages of CCFLs compared with the hot electrode fluorescent lamps are that they have a very long life (usually) 15000 hours or more) in consequence of their rugged electrodes, lack of filament and low current consumption. They start immediately, even under cold ambient conditions. Their life is unaffected by the number of starts. Also, they may be dimmed to very low levels of light output.
U.S. Pat. No. 4,650,265 issued Mar. 17, 1987 to Holtzman teaches an illuminating lamp assembly for retrofitting an exit sign. This invention is directed towards a retrofit system with a rotatably threaded electrical connector for interfacing with an existing standard home-type incandescent light bulb electrical socket and a standard non-CCFL bulb and retaining arms configuration horizontally and rotatably mounted to the electrical connector.
U.S. Pat. No. 5,018,290 issued May 28, 1991 to Kozek et al. Teaches an exit sign with a plurality of low voltage incandescent lamp mounted on a printed circuit board to provide illumination from within a housing. Stenciled images are used on the external, semi-transparent housing surfaces. to reflect light emitted from the diodes relatively uniformly across a diffuser which further contributes to relative uniform transmission of light therethrough. The system uses low direct voltage diodes.
U.S. Pat. No. 5,388,357 issued Feb. 14, 1995 to Malita teaches a kit using LED units for retrofitting illuminated signs. The kit retrofits a conventional exit sign, which normally uses internally mounted incandescent or fluorescent lamps, to operate using multiple LED sources in a group or assembly on a board. Indicia lighting is accomplished substantially indirectly through reflection of light from the LED sources which are powered through an adapter that fits into the socket of the original incandescent lamp or fluorescent lamp which is removed in the retrofit process.
U.S. Pat. No. 5,410,453 issued Apr. 25, 1995 to Ruskouski teaches a lighting device used in an exit sign. A light emitting diode lighting device is provided for mating engagingly with an electrical socket of the lighting fixture. The light emitting diode device has a plurality of LEDs recessed in frustoconical apertures for directing light into a desired illumination pattern.
U.S. Pat. No. 5,416,679 issued May 16, 1995 to Ruskouski et al. Teaches a mounting base assembly for a lighting device used in an exit sign. In the lighting fixture such as an exit sign, a mounting base assembly is provided on a light emitting diode lighting device for mating engagement with an electrical socket. Once full mating engagement is achieved between the electrical socket and a base member of the mounting base assembly, the position of the housing carrying the light emitting diodes of the lighting device can be adjusted for alignment purposes without disturbing the full mating engagement of the electrical socket and the base member.
U.S. Pat. No. 5,428,515 issued Jun. 27, 1995 to Jung teaches an electric lighting assembly. The assembly included a protective holder formed on the top with two holes and at two opposite sides with depending lugs, said lugs having a hook portion at the lower end, a ring contact secured on the top of said protective holder. A contact is provided on the top with a tip contact and the outer peripheral wall with spiral threads, said tip contact and said spiral threads being electrically connected with the two holes of said protective holder, a conical member connected with the two holds of said p protective holder and supported by the hook of said lugs, and a neon light bulb connected with said conical member, whereby the neon light can be used indoors.
LED 8 ½″ Red Signal & Retrofit Kit, Econolite Control Products; Inc., Anaheim, Calif. (undated, 2 pages). This signal head section uses a circuit board with 420 to 675 individual ultra-bright red 2000 mcd LEDs to replace the conventional lamp, socket and reflector assembly of a conventional 8 ½″ incandescent red signal head. It is powered directly by 120 volts alternating current. Because the LEDs are packed more densely in the center, it is nearly indistinguishable from its incandescent counterpart in brightness, color and viewing angle. Visibility is excellent, even in bright sunlight. A wide viewing angle is achieved with the use of a faceted red lens.
U.S. Pat. No. 5,440,467 issued Aug. 8, 1995 to Lautzenheiser teaches a task light. The light assembly is provided for illuminating a work surface below and in front of the light assembly, and includes a housing configured for mounting over the work surface with an elongated linear light source supported in its housing. A tubular lens is built into and part of the housing, and includes prism-shaped triangular rings on its inside surface for controlling the light from the light source onto the work surface therebelow.
Exit signs are currently illuminated with a variety of light sources in a variety of methods. The electric light sources currently include incandescent, compact and tubular fluorescent lamps, electro-luminescent (EL lamps and light emitting diodes (LEDs). LED technology offers low power consumption, long lamp lives, and low maintenance requirements. With LED illuminated signs, annual energy and maintenance costs can be reduced by more than 90% compared to a typical sign using incandescent lamps. LED technology represents the greatest improvement over incandescent and compact fluorescent lamps. However, there are many limitations to performance inherent with LEDs. Performance of LEDs in illuminated signage and traffic signals is limited because LEDs emit light directionally and only in discrete colors, such as red, green and yellow. Red has the highest lumen/watt output, while green and the other colors emitted by LED drop off to about 30% of the red lumen level. Due to the directionality of the light output of LED and the color limitations, applications are restricted. Due to the variable brightness, green and other colors are not readily adaptable in may applications. More LEDs are needed to equal the luminosity of the red LED. Space restraints come into play and wattage consumption goes up accordingly.
CCFLs emit white light omnidirectionally, while combining low power consumption, long lamp lives, and low maintenance requirements similar to LEDs. Light outputs remain constant for all colors, not like LEDs whose light output varies with each color. The omnidirectional white light output is a key factor in the present invention.